Manually collecting and refreshing statistics for a DDL table

This is how to manually update the statistics used by the SYSCOLUMNSTAT View for a SQL DDL table, TESTABLE.

If the video is too small for you to see what is going on, click on the YouTube link in the video, or click here.

 

IBM documentation describing how to do this here.

 

Using ACS version 1.1.9.1

More useful information added to SYSCOLUMNSTAT View about variable length columns

As part of the recent IBM i Technology refreshes, 7.5 TR1 and 7.4 TR7, three new columns were added to the SYSCOLUMNSTAT View. These are only of interest for variable length columns. While two of the columns I found easy to understand the third took awhile for me to work out what its contents mean.

These new columns are:

• MAXIMUM_COLUMN_LENGTH:  For variable length columns this is the maximum length of the column. For fixed width columns this is the column length.

Converting numbers and characters into timestamps

I am sure we have all worked with ERP Applications that still store their dates and times in numeric or character fields. I was asked what would need to be done to convert these into a timestamp in a SQL Select statement. Personally, I do like using timestamps rather than individual date and time columns, or fields. Therefore, I consider this a good question.

I have a SQL DDL Table with a mixture of "date" and "time" columns within it:

• DATE_NBR8:  A numeric representation of a date, eight long, and in ISO format (YYYYMMDD).
• DATE_NBR7:  A numeric representation of a date, seven long, in CYMD format (CYYMMDD).
• DATE_CHAR:  A character representation of a date, eight long, in ISO format with no separator characters.
• DATE_DATE:  What I would call a "true date", date data type.
• TIME_NBR:  A numeric representation of a time, six long.
• TIME_CHAR:  A character representation of a time, six long, with no separator characters.
• TIME_TIME:  A "true time", time data type.

Find the most recent rows for a repeating sets of data with SQL

This post is based upon something I needed to provide to my superiors at my work. We have a history file that contains many thousands of repeating sets records (yes, I know it is time to purge the old data), I was asked to "create a SQL statement" that would return the most recent records for each key. It will make more sense when I show the data I am going to be using here.

In these examples the file is named TESTFILE, and contains three columns of data. I can use the following SQL statement to list the contents of this file:

01 SELECT * FROM TESTFILE

The results are:

Getting the hours, minutes, and seconds from a difference in timestamps with SQL

I have timestamp columns in a Db2 Table that I need to give the difference in hours, minutes, and seconds. Preferably I would put these into separate columns that I can then use in various ways in subsequent jobs and programs.

All you really needs to know about the Table I will be using is that it is called TESTTABLE, and the timestamp columns I need to calculate the difference between are:

1. FROM_TIMESTAMP
2. THRU_TIMESTAMP

I can easily determine the difference between the two with the following SQL statement:

Improved SQL built in function for calculating difference between timestamps

I had written about the Db2 built in function TIMESTAMPDIFF, which is used to calculate the difference between two timestamps and return the difference in various different units of time. In the latest Technology Refreshes, IBM i 7.5 TR1 and IBM i 7.4 TR7, a new and improved built in function, TIMESTAMPDIFF_BIG, was introduced.

TIMESTAMPDIFF had issues in being able to correctly return the difference in microseconds. IBM's documentation says that the new TIMESTAMPDIFF_BIG will do that correctly. The syntax of the two built in functions, BiF, is the same:

Copying data with an Identity column from one table to another and not change the value

It has always been a problem with copying data from one SQL DDL table to another if the table contains an identity column. Identity columns are controlled by the database itself. When a new row is inserted into the table the database assigns the Identity column in the new row the next sequence number. They are a great way to ensure that the table has a unique key, and they can be shared with other files as an external key to link back to the original table.

The issue has always been that if I copy data from one table to another with an Identity column of the same name the database will assign the inserted rows new identity values using the sequence of the copied to table. This has been a great frustration to us all, and has led to many forsaking Identity columns altogether.

How to change someone's PDM defaults

I have been asked this question twice this week:

Is there a way to change everyone's PDM settings without them having to into their own settings and making the change themselves?

Both people want to change the "file" that contains these setting either with a SQL statement or they would write a program to do so.

I do not know where the PDM settings are stored. I assume they are in a file, or possibly even files. As the data is IBM's data I would be very wary to change it as I have no idea of what the consequences are if I was to make a mistake.

Easy way to validate if user has a certain group profile

This is another example of something I found by accident. Checking IBM's documentation I can find that this is found in IBM i releases 7.5 – 7.1, it might even be in earlier releases but IBM's online documentation only goes back to IBM i 7.1.

VERIFY_GROUP_FOR_USER is a SQL function that allows me to verify if the user of the current job is a member of any group profiles.

I could use the Display User Profile command, DSPUSRPRF, to display which groups and supplemental groups an user profile has. What is the fun in that when I can get the same information using SQL?